The invention relates to vehicle safety, and more particularly to a safety back-up system for normally preventing any backward movement of a vehicle such as a dump truck or a garbage truck unless an attendant is near the rear of the vehicle directing its movement, and to an associated system for stopping a moving vehicle whenever the driver leaves the seat, to prevent runaway accidents.
Trucks such as garbage trucks and dump trucks are known to collide rather frequently with stationary objects and structures behind the truck when the truck is backing up while on the job. Regulations of municipalities or of the trucking companies themselves normally require an attendant to be standing near the rear of the vehicle whenever it is being backed up, to direct the movement of the vehicle and avoid any such collisions. However, these rules are often circumvented for expediency, and the cumulative damage resulting from collisions from non-observance of these rules has been surprisingly large. One garbage disposal firm in the San Francisco Bay Area has experienced approximately 70 to 80 back-up accidents per month.
One attempted solution to this problem was a system marketed by Global Fabrications of Ontario, Canada. The system, mounted on a garbage truck or other vehicle, sensed objects approximately 45 inches to 50 inches behind the rear of the truck when the truck was moving backward, and automatically locked the brakes in response to sensing such objects. However, the system was not really practical on rear end loading trucks, and also the sensor and brake application device was only active when the truck was in reverse gear, excluding instances of rolling back on an incline, whether deliberately or by accident, without the truck being in gear. Moreover, the driver may actually want to back his vehicle to within a foot or two of an object or structure, which the prior art system would not permit, and a system of this sort really could not solve the real problem of assuring that the vehicle is properly directed from behind while backing.
The following prior art patents have some pertinence to the present invention: U.S. Pat. Nos. 4,142,152, 3,728,676, 3,783,339, 2,606,281, 2,961,640, 4,013,875 and 4,158,833. U.S. Pat. Nos. 4,142,152 and 3,728,676 disclose motion sensing arrangements for use on vehicles, including means for sensing motion via the rotation of a shaft in the reverse direction. The latter of these two patents discloses activation of a back-up alarm in response to sensing of reverse movement. U.S. Pat. No. 3,783,339 also signals the direction of travel of a vehicle, and the disclosed system is effective to apply brakes under certain conditions. U.S. Pat. No. 2,606,281 discloses a vehicle signalling device particularly for railroads, wherein the condition at a crossing is signalled to the moving train. If no signal is received to indicate a desired condition, the train's brakes are automatically applied. U.S. Pat. No. 4,013,875 shows an automatic vehicle control system including a back-up system with a form of override available to the operator.
Although several of the devices of the prior patents accomplish similar ends as in the present invention with respect to detecting backing motion in a vehicle, the principles involved in that motion detection are different from the present invention. In particular, U.S. Pat. Nos. 3,728,676 and 4,142,152 employ reed switches for sensing magnetic field from a permanent magnet which they pass. This differs from the present invention in structure and principle.
Moreover, no prior vehicle reverse sensing device has incorporated the other important features of the system of the present invention described below, for providing a reliable safety device for preventing back-up accidents and runaway accidents in service vehicles such as garbage trucks.